Vehicles powered by internal combustion engines have at least one fuel tank which generally holds a supply of liquid fuel for the engine. The tanks are typically connected to a filler tube which is used to introduce fuel into the tank. The outer opening of the filler tube is usually covered with a removable cap.
When fuel is added to the tank it displaces the air therein. The air, which is laden with fuel vapor, rushes out of the tank as the fuel enters. In many situations, foam is created by agitation of the fuel entering the tank. In some vehicles, the displaced air and foam rushes back out the filler tube as the tank is filled and splashes out on the person filling the tank. Other fuel systems include a vent line which extends from the interior of the tank to atmosphere. The vent line enables air to escape from the tank as it is filled with fuel through the filler tube. The vent line also enables air to enter the tank as fuel is withdrawn for delivery to the engine.
The fuel tank vent line also serves to prevent pressure from building in the tank. If the tank were unvented, increasing temperature of the fuel would cause fuel and vapor expansion which would cause the pressure in the tank to rise. If the pressure became too high, the fuel tank could rupture causing fire or explosion.
Fuel systems used on marine craft usually include a vent line from the fuel tank. The vent line typically opens to the atmosphere over the water. As the fuel tank is filled to near the top, the air flowing out of the vent line can carry fuel and foam overboard on to the water. Wave action which rocks a boat can also cause fuel to be discharged overboard both during fueling and when the tank is full. Fuel discharged overboard poses a pollution hazard and is harmful to wildlife. There is also a risk that fuel floating on the water may catch fire causing injury to life or property.
Government and trade organizations regulate the construction and operation of marine craft. These organizations include the U.S. Coast Guard, the National Marine Manufacturer's Association and the American Boat and Yacht Council. Manufacturers of pleasure boats who have their products approved by the American Boat and Yacht Council comply with standards which cover gas and diesel fuel systems known as H-24 and H-33 respectively. Proposed revisions to these standards include requirements for a fuel vapor separator in the vent line. Such separators must continuously vent the fuel tank to atmosphere while returning liquid fuel which enters the vent line back to the tank. The proposed standards also require that pressure inside the fuel tank not exceed 2.4 p.s.i.g.
A prior art fuel/vapor separator owned by the assignee of the present invention is disclosed in U.S. Pat. No. 4,963,169. This invention is designed to separate liquid from vapor in the vent line and to enable the liquid to flow back into the tank by gravity action. The separator shown in this patent works well but may still be unable to contain a fast moving slug of fuel, resulting in the discharge of fuel overboard.
There are also a number of prior art patents that show devices for separating liquid and recovering vapor. However, none of these are specifically adapted to be installed in a fuel tank vent line to vent the fuel tank to atmosphere while preventing the discharge of liquid fuel through the vent line.
U.S Pat. No. 3,981,156 discloses a vapor recovery system which includes a vapor scrubber that recovers storage tank exhaust vapors in a closed system by absorption in a refrigerated spray. This system avoids exhausting any vapor to atmosphere. The system disclosed in this patent is complex and unsuitable for use in marine fuel tank vent lines.
U.S. Pat. No. 4,769,050 discloses a liquid separator assembly for separating oil from engine crankcase fumes. In the device shown in this patent, an oil fill tube also serves as a crankcase vent tube. A separate vent line is not used in this system because oil is not added to the fill tube at the high rates at which fuel is added to fuel tanks. In addition, lubricating oils do not present the same flammability problems as fuels. As a result, the system shown in this patent would not be suitable for use in a fuel tank venting application.
U.S. Pat. No. 4,809,863 shows a filler neck for an on-board fuel vapor recovery system. The neck assembly has a chamber between the interior of an outer hose and the exterior of a filler tube. Vapor from inside the tank flows through the chamber into a vapor flow passage, and from there into a vapor recovery canister. The vapor passageway has a float and a seat therein which is designed to prevent liquid from reaching the canister. If liquid fuel should backup into the vapor flow passageway, the float will block all flow therethrough. As a result, pressures can build in the tank. This is unacceptable in marine applications for reasons previously discussed.
Thus, there exists a need for a liquid separation and recovery apparatus that can trap liquid fuel in a vent line and return it to the fuel tank while preventing the build up of pressure inside the tank. There further exists a need for a device which can prevent the discharge of fuel in high flow situations and can return the separated liquid to the fuel tank b positive action.